1. Field of the Invention
The present invention relates to an assembling method to be carried out by an assembling robot and, more particularly, to an automatic position-finding assembling method for inserting an insert member into a mating hole of a receiving fib when assembling a predetermined assembly, and an automatic position-finding assembling apparatus for carrying out the method.
2. Description of the Related Art
A multiple disk clutch is one of assemblies that are assembled by a position-finding assembling method. The multiple disk clutch is formed by alternately placing inner disks (receiving members), i.e., internally toothed disks, and outer disks, i.e., externally toothed disks, in a space defined by a cylindrical member. Both the inner disks and the outer disks are flat annular members and have center openings, respectively. Each of the inner disks is provided with a plurality of internal teeth on its inner circumference while each of the outer disks is provided with a plurality of external teeth on its outer circumference. The inner circumferences of the inner disk and the outer disks form a substantially cylindrical space. A shaft (insert member) provided on its outer surface with a plurality of axial splines is inserted in the substantially cylindrical space with the splines thereof engaging the internal teeth of the inner disks. The cylindrical member is provided in its inner circumference with a plurality of grooves. The external teeth of the outer disks engage the plurality of grooves of the cylindrical member.
When assembling the multiple disk clutch, the inner disks and the outer disks are inserted alternately in the space in the cylindrical member with the external teeth of the outer disks engaging the grooves of the cylindrical member, and then the shaft is inserted in the substantially cylindrical space defined by the inner and the outer disks. More concretely, the shaft is turned properly to find an angular position where the splines of the shaft are able to engage the internal teeth of the outermost inner disk, and the shaft is inserted in the center opening of the outermost inner disk. Subsequently, the shaft is advanced into the substantially cylindrical space and the shaft is turned together with the outermost inner disk engaged with the shaft and is properly moved axially back and forth to find an angular position where the spines of the shaft are able to engage the internal teeth of the second outermost inner disk. Thus, an operation for finding an engaging position where the splines of the shaft are able to engage the internal teeth of the inner disk and an operation for inserting the shaft into the center opening of the inner disk are repeated alternately to assemble the multiple disk clutch.
When thus assembling the multiple disk clutch, the inner disks are not restrained at all from movement in the cylindrical member and the positions and the angular positions of the inner disks are variable before the shaft is inserted in the inner disks. Consequently, the inner disks move away from the shaft and the internal teeth of the inner disks are dislocated from an engaging position where the same are able to engage the splines of the shaft. Therefore, operations for finding an engaging position where the splines of the shaft are able to engage the internal teeth of the inner disks and for pushing the shaft into the openings of the inner disks must unavoidably depend on the feeling of a skilled hand.
Attempts have been made to carry out such assembling operations automatically by an assembling robot. An assembling method that guides a shaft, i.e., an insert member, into the tapered receiving hole of a workpiece, i.e., a receiving member, and an assembling method that aligns an insert member with the receiving hole of a receiving member by a simple groping reciprocating operation of a mechanism are proposed in JP-A Nos. 57-184639 and 62-204035.
Although the prior art assembling method that tapers the receiving hole of a workpiece is effective in expanding the range of positions of the insert member relative to the receiving hole of the receiving member where the insert member can be inserted in the receiving hole, this assembling method require subjecting the receiving member to a functionally unnecessary machining process and requires changes in design. The assembling method that uses simple groping reciprocating operation needs a special hand for assembling an assembly of an insert member and a receiving member, and needs different special hands for assembling different assemblies. When the assembling mood that uses the simple groping reciprocation is applied to assembling, for example, a multiple disk clutch, friction disks are liable to move together with a shaft or the shaft is liable to be caught by the friction disks and becomes immovable. Consequently, it takes a long time for finding the internal teeth of the friction plate and hence the assembling work cannot be precisely and quickly carried out.
The present invention has been made in view of those problems and it is therefore an object of the present invention to provide an automatic position-finding assembling method for assembling an assembly by inserting an insert member into a mating opening of a receiving member, capable of quickly and surely finding an engaging position where the insert member is able to engage the receiving member and of precisely and quickly carrying out assembling work, and an automatic position-finding assembling apparatus for carrying out the method.
According to a first aspect of the present invention, an automatic position-finding assembling method for inserting an insert member held by an end effector of an assembling robot into a mating opening of a receiving member to assemble a predetermined assembly, comprises the steps of: positioning the insert member relative to the mating opening of the receiving member by moving the insert member held by the end effector relative to the receiving member; and pressing the insert member against the receiving member by a pressing force applied to the insert member in a direction parallel to a third axis by the end effector compliant with respect to directions parallel to first and second axes perpendicular to the third axis; wherein in the step of pressing the insert member against the receiving member, the compliance center of the insert member is moved along a predetermined groping route with the pressing force applied to the insert member in the direction parallel to the third axis by the end effector.
In the automatic position-finding assembling method in the first aspect of the present invention, it is preferable that the groping route is set for repetition of a radially outward movement from a position near the center of the mating opening of the receiving member in different phases in a plane defined by the first and the second axes.
In the automatic position-finding assembling method in the first aspect of the present invention, it is preferable that the groping route is a cloverleaf route expressed by the following expressions representing x and y coordinates on a plane defined by the first axis as x-axis and the second axis as y-axis:
x=Ax{sin(xcfx89t)+sin(nxcfx89t)}
y=Ay{cos(xcfx89t)xc2x1cos(nxcfx89t)}
where Ax and Ay are amplitudes (leaf size), n is a real number (relating to number of leaves), xcfx89 is a velocity of groping motion and t is time. Please note that n is a real number and not necessarily an integer.
In the step of pressing the insert member against the receiving fiber in the automatic position-finding assembling method in the first aspect of the present invention, it is preferable that the pressing force produced by the end effector is reduced during the movement of the compliance center of the insert member along the grouping route. It is preferable that the insert member held by the end effector is rotated periodically about its axis in the step of pressing the insert member against the receiving member. It is preferable that the compliance is exercised through the compliance control of the end effector.
In the automatic position-finding assembling method in the first aspect of the present invention, it is preferable that the insert member is a shaft having engaging portions formed on its outer circumference, the receiving member includes a plurality of plate-shaped members each having a center opening provided on its circumference with engaging portions mating with the engaging portions of the shaft, and the plurality of plate-shaped members are arranged with the center openings thereof aligned with each other.
According to a second aspect of the present invention, an automatic position-finding assailing apparatus for inserting an insert member into a mating opening of a receiving member by an assembling robot to assemble a predetermined assembly, comprises an end effector for holding the insert member; and a control unit for controlling the operations of the end effector so that the insert member held by the end effector is inserted in the mating opening of the receiving wherein the control unit gives the end effector compliance with respect to directions parallel to first and second axes perpendicular to a third axis extending in a direction in which the insert member is moved for insertion, and a compliance center of the insert member is moved along a predetermined groping route with a pressing force applied to the insert member in a direction parallel to the third axis by the end effector.
According to the present invention, the insert member is pressed against the receiving member by the end effector having a compliance and the compliance center of the insert member is moved along the predetermined groping route. Therefore, the mating opening of the receiving member can be found by actively moving the insert member in the plane perpendicular to the direction of insertion and hence an engaging position where the insertion member is able to engage the receiving member can be surely found in a short time. Since the end effector is compliant, any excessive force is not applied to the insertion member and the receiving member while the insertion member is moved for grouping along the groping route and the breakage of the engaging portions of the insertion member and the receiving member can be prevented.
According to the present invention, the insert member can be temporarily separated from the receiving member and the position finding operation of the insert member can be resumed by temporarily reducing the pressing force exerted on the insert member by the end effector during the position finding operation. Accordingly, the present invention is capable of surely dealing with a case in which the receiving member moves together with the insert member, and the insert member is unable to reach an engaging position where the same is able to engage the mating opening of the receiving member. In other words, the present invention is capable of dealing with a case in which the engaging position where the insert member is able to engage the mating opening of the receiving member cannot be found in a predetermined time.
According to the present invention, the angular misalignment of the engaging portions of the insert member relative to engaging portions of the receiving can be corrected by periodically rotating the insert member held by the end effector about its axis. Consequently, the present invention is capable of surely dealing with a case in which the engaging portions of the insert member are dislocated relative to the engaging portions of the receiving member so greatly that the engaging portions of the insert member cannot be aligned with those of the receiving member by the agency of the compliance of the end effector.
The compliance can be given to the end effector though the compliance control (execution of a control algorithm by the control unit) without providing the end effector with any complicated compliance mechanism, so that the assembling work can be carried out by a simple mechanism.
According to the present invention, the groping route is set for repetition of a radially outward movement from a position near the center of the mating opening of the receiving member in different phases in a predetermined plane. Therefore, the compliance center of the insert member moves radially outward from the position near the center of the mating opening of the receiving member in different phases. Thus, the engaging position where the insert member is able to engage the receiving member can be surely found even if the center of the mating opening of the receiving member is dislocated or the compliance center of the insert member is in contact with a portion of the receiving member and does not correspond to the center opening of the receiving member in an initial state. Particularly, when the groping route is the cloverleaf route expressed by the foregoing functions, the insert member can be smoothly moved, the groping route can be easily set, and even a low-function controller is able to carry out sufficiently precise work because the groping route can be calculated by using simple, handy trigonometric functions to reduce load on the control unit when producing a command signal.